The answer to the Web's most annoying question has been revealed. GM's viral "what is 230?" marketing campaign littered Twitter and Flickr, YouTube, blogs, Facebook, and cable for days, and now we finally know what it means.The embattled automaker announced Tuesday that it expects its long-awaited Chevrolet Volt to get 230 MPG in city driving "based on development testing using a draft EPA federal fuel economy methodology for labeling for plug-in electric vehicles," according to GM's press release.

Development. Testing. Draft. Hmmm. That is a great big bowl of hedge, and GM acknowledges it. "Actual testing with production vehicles will occur next year closer to vehicle launch," said Frank Weber, global vehicle line executive for the Volt in a statement.

To compare, the 2010 Toyota Prius is rated at 51 mpg in city driving and 48 mpg on the highway.

A triple-digit MPG is impressive, but sadly for GM, 230 comes up short in comparison to Nissan's all-electric Leaf. The Leaf is slated to be in showrooms late next year, as much as a full year ahead of the Volt. On Tuesday, like a bucket of ice water on GM's head, Nissan trumpeted the DOE's estimate for the Leaf: 367 MPG.

Showing that GM isn't the only car company with social networking skills, Nissan EVs on Twitter tweeted Tuesday: "Nissan Leaf = 367 mpg, no tailpipe, and no gas required. Oh yeah, and it'll be affordable too!"

To the further consternation of GM, the Leaf is expected to be priced between $25,000 to $33,000 -- significantly lower than the Volt's anticipated $40,000 price tag.

The real truth about MPGs is still out there. Anyone who has ever driven a new car off a lot knows that the EPA numbers are, as one blog commenter put it, "whack." The DOE and EPA have yet to determine standards for measuring hybrids and all-electric vehicles and place them in a context resembling reality.

Until then GM's and Nissan' mileage will vary -- and so will yours.